1. The Field of the Invention
This invention relates to electrical heaters and, more particularly, to novel systems and methods for applying conductive coatings to substrates.
2. The Background Art
The semiconductor manufacturing industry relies on numerous processes. Many of these processes require transportation and heating of de-ionized (DI) water, acids, and other chemicals. By clean or ultra-pure is meant that gases or liquids cannot leach into, enter, or leave a conduit system to produce contaminants above permissible levels. Whereas other industries may require purities on the order of parts-per-million, the semiconductor industry may require purities on the order of parts-per-trillion. Ultra-pure may be considered to be a purity level having contaminants at concentrations of one hundred parts-per-billion or less.
Chemically clean environments for handling pure de-ionized (DI) water, acids, chemicals, and the like, must be maintained free from contamination. Contamination in a process fluid batch may destroy hundreds of thousands of dollars worth of product. Several difficulties exist in current systems for heating, pumping, and carrying process fluids (e.g. acids, DI water). Leakage into or out of a process fluid conduit must be tightly controlled and preferably eliminated. Moreover, leaching and chemical reaction between any contained fluid and the carrying conduits must be tightly controlled and preferably eliminated.
Elevated temperatures in semiconductor processing are often over 100 C, and often sustainable over 120 C. In certain instances, temperatures as high as 180 C may be approached. It is preferred that all process fluid heating and carrying mechanisms virtually remove the possibility of contact with any metals, regardless of the ostensibly non-reactive natures of such metals. It is desirable to prevent process fluid contamination, even in the event of a catastrophic failure of any element of a heating, transfer, or conduit system.
Conventional immersion heaters place a heating element, typically sheathed in a coating, directly into the process fluid. The heating element and process fluid are then contained within a conduit. Temperature transients in immersion heaters may overheat a sheath up to a melting (failure) point. A failure of a sheath may directly result in metallic or other contamination of the process fluid. Meanwhile, temperature transients in radiant heaters may fracture a rigid conduit.
A heating alternative is needed that does not have the risks associated with conventional radiant and immersion-heating elements. A system is needed that is both durable and responsive for heating process fluids. Failure that may result in fluid contamination is an unacceptable risk.